When you're running in a full on sprint, regardless of being a mutated Witcher or not, you still abide by the laws of physics, you do not go from a full sprint to a sudden stop without moving or doing something to transfer that force.
However I just hope the keep the sense of weight if they change it to show that Geralt has weight and his movement doesn't feel "floaty" or unnatural like it would if they simply had him going from resting>sprint without animation or from sprint>full stop by simply having him "stop" with no animation to show this.
Er, what? You don't see athletes taking a step or three before they start running. In fact, my neighbours probably think I'm a bit of a twat since I just ran back and forth across the floor just to prove to myself that you can, in fact, go from standing still to sprinting without any walking steps in between. Stopping is a lot harder, particularly with socks on a hardwood floor, but on a better surface providing actual traction that wouldn't be a problem either. There is a difference between heavy and clunky. Dark Souls is heavy. A bit too heavy at some points since the attacks invariably consist of wide, slow swings that wouldn't make sense in real life. But it's never really clunky. The closest you get to clunky is rolling in heavy armour, where it's intended. Other than that the movement and combat is really responsive, unlike this game.